1. Technical Field
This invention relates to hydraulic hand tools, and more particularly, to a hydraulic tool that can use a constant pressure fluid delivery system or a constant volume fluid delivery system. In particular, this invention relates to a hydraulic tool having a selector switch to operate the tool in an “open center” (OC) mode or a “closed center” (CC) mode.
2. Description of the Prior Art
Hand held hydraulic tools capable of operating by two different modes of operation known as constant volume and constant pressure are disclosed in the prior art such as U.S. Pat. No. 4,366,673, issued Jan. 4, 1983 to Lapp. That patent shows an apparatus having a valve body with a pressure port 25 and a return port 26, a cross port 31 and a tubular conduit 72, a valve spool 45, and a selector member 63 in which the plug 63 enables the valve 45 to be converted so that the amplifier 13 may be used with either an open center or a closed center pump system (see column 4, line 54).
A closed-open center hydraulic valve assembly is shown in U.S. Pat. No. 3,882,883, issued May 13, 1975 to Droegemueller.
The term “constant volume” refers to the fact that there is an open center spool valve. In such an arrangement, oil flows back to the source through the spool in what is known as the neutral or off position.
In a constant pressure tool, a closed center spool prevents the oil from flowing back, thereby maintaining the pressure.
U.S. Pat. No. 5,442,992, issued Aug. 22, 1995 to Sanner, et al., discloses a hydraulic tool which has a rotatable selector 60, FIG. 1. In the constant volume (OC) mode, fluid flows on the back side of the piston and around the piston through a passage 62 having a check valve therein permitting fluid flow in only one direction from a cross-port 52 to the opposite end of the tubular conduit.
U.S. Pat. No. 6,490,962, issued Dec. 10, 2002 to Schultz, discloses a hydraulic tool in which a selector sleeve 5 may be moved so that oil can pass through a hole 12 in the tube 6 which is coincident with a hole 9a in a sleeve valve 9 in the constant volume (OC) mode neutral position, as shown in FIG. 3. In order to move this sleeve, it is necessary in practice to back off a set screw (shown in the Figure but not identified in the description of the patent specification), so that two portions butt up against one another and the spring 13 is compressed. This selector sleeve provides for switching between the OC and CC modes.
This patent shows, discloses and claims a hydraulic tool adjustable between two modes of operation. One mode is known as the open center mode, or constant volume mode; and the other mode is known as a closed center mode, or constant pressure mode. Each mode has both a neutral position and a work position.
The constant pressure neutral position is shown in FIG. 1 wherein pressurized fluid travels through a tube into a retract chamber.
When the trigger 20 is squeezed, the configuration is as in FIG. 2. This is the working position when the hydraulic fluid flows into a drive chamber 4 causing the piston 2 to move to the left, and exhausting fluid which was in the retract chamber 3 to exhaust through the central tube out an exit port 15.
In the constant volume mode, the neutral position is shown in FIG. 3 wherein fluid passes through a central tube 6 and into the retract chamber 3. At the same time, the excess fluid exits through a small hole 12 between the ends of the tube 6 and then out through the exit port before ever reaching the drive chamber 4.
When the trigger is pulled, the working position is as shown in FIG. 4 which is identical to the working position in FIG. 2, that is, the fluid passes directly into the drive chamber. In this mode, fluid exits just as it did in FIG. 2 down the inner tube and out the exit port 15 from the retract chamber.
U.S. Pat. No. 5,778,755, issued Jul. 14, 1998 to Boese, also discloses a hand-held and operated hydraulic tool with a control valve having a sensor switchable between an open end and closed condition. The adjustment assembly provides a structure which can be configured to force open shuttle spool valves in the control apparatus in a neutral condition for use with a constant volume power supply. The adjustment assembly can also be configured to be disengaged from the shuttle spool valves in a neutral condition for use on a constant pressure hydraulic power system.